(1) Field of the Invention
The present invention relates to the identification of a single closed switch in a switch array and particularly to the provision of both visual and coded electrical indicia commensurate with such a closed switch. More specifically, this invention is directed to logic circuitry which may be associated with plural, parallel connected switches for providing a coded signal which identifies a closed switch while simultaneously causing energization of a light emitter associated with the closed switch. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The present invention is particularly useful with circuits known in the art as "tip switch banks". A "tip switch bank" comprises a plurality of switches wherein actuation of the switch contacts, i.e., making or braking, results from touching or "tipping" only. The switches comprising the "bank" may, for example, be momentary contact type switches or some other type of touch sensitive switch. The switches forming the "bank" may be functionally interrelated such that only the last switch "tipped" by the user is "valid" or enabled while all other, i.e., formerly actuated, switches are rendered "invalid" (disabled or cancelled). In this case, the switches of a "tip switch bank" are electrically mutually latched and only a single switch will at any one time be in the "actuated" state. In any case, however, each switch of the "bank" is provided with a light emitter, for example an indicator lamp, which will visually signal the state of its associated switch. In the typical case, the light emitter associated with the last switch of the "bank" to have been actuated will be energized.
"Tip switch banks" of the type briefly described above are frequently employed in electronic organs as the user input which determines the sound coloration when conventional musical instruments of different nature are to be simulated. Thus, a signal which identifies the last actuated switch will be employed to address a controlled circuit such as a filter, memory or the like to cause production of the audible output commensurate with the actuated switch.
In prior art "tip switch bank" control circuits the indicator lamp associated with each switch is allocated to one of the parallel outputs of a shift register. Binary data was serially shifted through the register under supervision of a control unit. The contents of the shift register were "permanently" available at the parallel outputs thereof in the form of "high" and "low", i.e., binary, voltage levels. The light emitting indicators were all also connected to a common bus which had applied thereto either the binary "high" or "low" voltage level. Thus, if the "high" or binary "1" voltage level is applied to the bus, an output of the shift register which has a binary 0 appearing thereon will result in the light emitter connected to that output being energized since there will be a sufficient potential difference across the light emitter to cause current to flow therethrough. With no switch actuated, all of the parallel data outputs of the shift register will be "high" and thus current will not flow through the light emitters associated therewith. The state of the output of the shift register will be read out as address information for a controlled or circuits such as filters, memories or the like.
Thus, in accordance with the prior art, upon actuation of one of the "tip switches" a control unit will load the shift register with binary data corresponding to the actuated switch. If another switch is "tipped", this fact must be signalled back to the control unit so that it may update the loading of the shift register. This signaling has previously been accomplished by individually connecting each switch to the control unit. Alternatively, all of the switches of the "bank" were scanned by means of a separate multiplexer. In either case the resulting circuitry is comparatively complex, particularly when the "bank" comprises a large number of switches.